If someone would like to have unique planks on top of the treasure chest. And not use the mirror modifier. I noticed that when you Link the object data, the objects all rotate, even if you lock the rotation for example. So I wonder /how can I see the exact direction an normal is facing, so after the linking, I can check that normal again and correct in manually.
Edit: after linking data I cannot separate any object with P. Maybe they only way is to copy (SHIFT+D) and place it in place
Like to keep the planks separate then all planks can be individually be used.
Linking Onject Data means, that all those Linked Objects share the same 'list' of where Vertices are in the Object's own Coordinate Systems:
Changing a Vertex in 1 of those Objects, changes it in all. You can Transform (Move, Scale, Rotate) each Object to get different looks, although the Objects are sharing the same Data, to vary the look of each Instance/ Linked Duplicate.
Using SHIFT+D Duplicates is just an awful lot of extra modeling work and with Linked Duplicates, you can still get loads of variation.
As a proof of that, this Scene only uses 5 different planks: https://cgcookie.com/projects/nelson-s-blood
You can use totally different and unique planks that you model one by one. Kent does it the way he does it in the tutorial, just so he can be effective and work smarted and be more effective with his time and effort. But if you can spend the time modeling unique planks, you can go for that approach. Of course the tutorial is set to show you how you can have enough variation with minimal effort.